Add checking of `TEXT MAX LENGTH` if it is set in the string's `description`

some strings has defined lenght limitations described in the `description` property

e.g.
base string:
```
"popup_modal_advanced_blocking_disabled_description": {
"message": "Advanced blocking rules and other extended features are not available. Read more<\/a>",
"description": "TEXT MAX LENGTH: 85"
},
```
translation:
https://uploads.adguard.org/slbdzdrvnt1kt.png

it could be checked during the translations validation